The leader of Syria's Al Nusra front has pledged allegiance to Al Qaeda boss Ayman al-Zawahiri in an audio message on Wednesday, whilst distancing the group from claims they had merged with Al Qaeda in Iraq, AFP reported.

"The sons of Al-Nusra Front pledge allegiance to Sheikh Ayman al-Zawahiri," Abu Mohammed al-Jawlani said in the message.

He also said "we were not consulted" on an announcement made by Al-Qaeda in Iraq chief Abu Bakr al-Baghdadi on Tuesday, that the groups had merged.

"We inform you that neither the Al-Nusra command nor its consultative council, nor its general manager were aware of this announcement. It reached them via the media and if the speech is authentic, we were not consulted," Jawlani added.

He stated the group would maintain its flag and not change its "behaviour."

"Al-Nusra Front will not change its flag, though we will continue to be proud of the flag of the Islamic State of Iraq (ISI), of those who carry it and those who sacrifice themselves and shed their blood for it," said Jawlani, who fought in Iraq alongside Al Qaeda's Iraqi arm.

"We reassure our brothers in Syria that Al-Nusra Front's behaviour will remain faithful to the image you have come to know, and that our allegiance (to Al-Qaeda) will not affect our politics in any way," he said.

The comments come after the ISI claimed that the Al Nusra Front was part of its network, vindicating US suspicion that the group was part of the jihadist network.

"It is time to declare to the Levant and to the world that the Al-Nusra Front is simply a branch of the Islamic State of Iraq," ISI's chief Abu Bakr al-Baghdadi said in an audio message.

The groups would be combined and called the Islamic State in Iraq and the Levant, Baghdadi said, describing Jawlani as "one of our soldiers".

"We chose al-Jawlani... as well as other fighters to go from Iraq to Syria... We prepared plans and work policies. We gave them money and personnel support," Baghdadi said.

The statement followed public calls from Al Qaeda leader Zawahiri for rebels to fight for an Islamic state.

The Free Syrian Army has maintained its distance from the Al Nusra Front, saying that they don't agree with their ideology.

"We don't support the ideology of Al-Nusra," FSA spokesman Louay Meqdad told AFP, stessing: "There has never been and there will never be a decision at the command level to coordinate with Al-Nusra.